1. Field of the Invention
This invention relates to tube couplings and is particularly although not exclusively applicable to tube couplings for potable water and domestic heating appliances.
2. Description of the Prior Art
Stringent regulations cover the use of couplings in potable water and domestic heating appliances and must be made from materials which are both hygienic where there is any possibility of contact with potable water and also rugged to withstand the different loads imposed. Traditionally materials which have been used for such couplings have been brass and cast iron but these are now becoming less acceptable to the relevant authorities.
Additional problems arise for couplings to be used for domestic central heating systems since the latter produce particularly corrosive acid/water mixtures which eat into many known materials otherwise suitable for such equipment. Materials such as polybutelene are considered to be satisfactory for such couplings but have the disadvantage that a significant curing time is required in the manufacture of couplings from such material and also a rather large section is required to provide adequate strength. Another possible material for such couplings is polyethelene but this has to have a substantial "soak" period of at least 24 hours in an autoclave.